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1. Explain the working of ARP?

Answer :

Address Resolution Protocol (ARP) is TCP/IP standard which is defined  in RFC 826. ARP used to resolve ip addresses with the help of TCP/IP software to media access control address with the help of hardware in LAN. ARP provides the following protocol to host which are in same network. Media Access control addresses can get from a network broadcast request . After ARP requests reply  both sender as well as receiver can get ip addresses and media accesses control . This record save in local table called ARP cache for references.

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2. What is the working of Spanning Tree Protocol?

Answer :

Spanning Tree Protocol is used to avoid loop and broadcast storm in the Local Area Network (LAN) . The Spanning tree protocol allows redundant links in the network to prevent network failure if any active link fails without any loop in  layer 2 switchings.

3.What is the difference between the broadcast domain and the collision domain?

Answer :

Broadcast Domain-

-Broadcast Domain is set of computers which are reachable without routers.

-It is limited to specific IP sub network for the IP broadcasts.

-It uses in switches for broadcast.

-In network systems we can have 255 at the end of Ip addresses

Collision Domain

-Collision Domain  is set of devices in which packet collision happened.

-Devices can include the devices of different ip sub networks.

-collision occur on cable ,hub and repeater.

-potential packet collision as multiple devices transmit traffic on one link.

4.Explain the steps in the Spanning tree Protocol?

Answer :

Blocking –  no any participation in frame forwarding

Listen –  This is the first step after the blocking. It determines that interface should forward the frame

Learn –  Interfaces are ready for frame forwarding

Forward  – Interface actually forward the frames.

Disable- Port is shut down so any any participation in frame forwarding

5.What is Root Port ?

Answer :

The root port is usually the link directly connected to the root bridge, or the shortest path to the root bridge. If multiple link connects to the root bridge, then a port cost is determined by checking the bandwidth of each of link. The lowest-cost port becomes the root port. If multiple links have an equivalent cost, the bridge with the lower advertising bridge ID is used.

6. What is Designated Port?

Answer :

A designated port is one that has been determined as having a more effective cost. A designated port will be marked as a forwarding port.

7. What is Rapid Spanning Tree Protocol?

Answer :

The convergence time for legacy Spanning Tree Protocol (STP) IEEE 802.1D standard is 30 to 50 seconds. When the network is intersected on a topology change, no traffic is forwarded to or from any of the network bridges and switches. In networks this convergence time gap is not acceptable and Cisco enhanced the original Spanning Tree Protocol (STP) 802.1D specification with features such as PortFast, UplinkFast and BackboneFast to speed up the convergence time. But these were proprietary enhancements.

The Rapid Spanning Tree Protocol (RSTP) IEEE 802.1W standard is available to address the convergence time gap issue. Rapid Spanning Tree Protocol (RSTP) enables root ports and designated ports to change from the blocking to forwarding port state in a few seconds.

8. Explain Per-VLAN Spanning Tree (PVST)  and Per-VLAN Spanning Tree Plus (PVST+).

Answer:

The type of a one instance Spanning Tree Protocol (STP) is nothing but Common Spanning Tree (CST). Delay in receiving BPDUs is common in big switched Common Spanning Tree (CST) networks. The delay in receiving BPDUs will cause issues like convergence time issues. Per-VLAN Spanning Tree (PVST) is  the best  solution for these problems. Per-VLAN Spanning Tree (PVST) is  Cisco proprietary Spanning Tree Protocol (STP) that operates a separate instance of Spanning Tree Protocol (STP) for every individual VLAN. A separate instance of Spanning Tree Protocol (STP) for every  VLAN helps VLAN to be configured independently and also can perform better. Per-VLAN Spanning Tree (PVST) requires Inter-Switch Link (ISL).

Per-VLAN Spanning Tree+ (PVST+) is extension of the PVST standard. Per-VLAN Spanning Tree+ (PVST+) allows interoperability between CST and PVST in Cisco switches and support the IEEE 802.1Q standard.

9. What is vtp change advertisement period time?

Answer :

Vtp probably take 300 sec nothing but 5min time to change the advertisement period.

10. Explain Vlan ?

Answer :

VLANs (Virtual LANs) is nothing but logical grouping of devices in the same broadcast domain. VLANs are generally configured on switches by adding some interfaces into one broadcast domain and some interfaces into another. VLANs can be included in  multiple switches, with each VLAN being treated as its own subnet or a broadcast domain. This means that frames broadcasted onto the network will be switched only between the ports within the same VLAN.

11. Explain Ether channeling?

Answer :

Ether channeling is nothing but logical bundling of multiple links to get higher bandwidth.

There are 2 types of Ether channeling

  1. Port aggregation Protocol (PAgP)

PAgP (Cisco proprietary) enables the Catalyst switches to learn the capabilities of each interface assigned to an EtherChannel group and activate interfaces of similar configuration to form a port-channel.

2. Link Aggregation Protocol (LACP).

LACP works in a similar to PAgP, only its multi-vendor or standard channeling protocol.

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12. What is DHCP snooping?

Answer :

DHCP snooping is a layer 2 security concept . DHCP snooping helps to prevent access of invalid DHCP servers. DHCP  service detects a violation.

13.Explain Port Security?

Answer:

When switch reaches the  limit for its mac address table it starts

flooding traffic out all ports like a hub. Hackers can fill switch mac address

table by sending thousands of spoofed mac addresses via one port, causing

switch eventually to flood each every traffic. This can degrade the traffic

performance. Also unnecessary flooding can be exploited by hackers, to sniff

the traffic passing in the environment.

A way to avoid this “mac address table poisoning” vulnerability is to use a

feature called “Port Security”.

Port Security is most important   layer 2 security mechanism that can limit the

number of mac addresses can  learned on a single switch port.

Port security can be configured on access and trunk ports and not on dynamic

desirable ports.

14 Explain different types of port security violation?

Answer :

Violation modes

It decides the action to be taken by switchport id port security rules are

violated.

  • Restrict

In restrict mode, port doesn’t shutdown, frames from non-allowed address would

be dropped. Switch will make a log entry and generate a snmp trap message

  • Shutdown

In this mode switch generate the violation alert and disable the port by

putting it in error-disable state.

  • Protect

In Protect mode, port doesn’t shutdown, frames from non-allowed address would

be dropped. Switch will not make a log entry.

 

15. Explain SNMP?

Answer :

Simple Network Management Protocol (SNMP) was evolved  in 1988 to manage IP networks.

There has been three updates to SNMP to provide enhanced features and security. SNMP is

available on nearly every networking equipment.

SNMP requires agents on a managed device to relay information to a management station. A

management station(NMS) will have an application running to manage devices. SNMP agent

uses a management information base (MIB) to organize object identifiers (OID). Each OID

represents a value which can be read or configured by SNMP.

16. Explain EUI in IPV6?

Answer : 

EUI-64  is nothing but Extended Unique Identifier .EUI allows the device to use its MAC address and pad it to make the interface ID. MAC address is padded in the middle with “FFFE” to form 64 bits interface ID , as MAC address is only 48 bits long. e.g. 1. MAC Address : 0060:d673:1987 Interface ID : 0260:d6FF:FE73:1987 The 7th bit is altered.

 

17. Explain AAA?

Answer:

AAA is nothing but Authentication,Authorization and Accounting

User Authentication and authorization from local database is suitable for

smaller networks. But for large network, we cannot configure all the users on

all the routers/switches; So we use the centralized database. It will store

usernames and passwords of all users.

Centralized database is known an “AAA server”

18. Explain Syslog?

Answer :

Syslog is a method to collect messages from network devices to a server running software to collect logs. Logging to a central syslog server helps in timely aggregation of logs and alerts. The following are four popular ways to gather messages from Cisco Devices: 1. Buffer Memory 2. Console line 3. Terminal lines 4. Syslog Serve.

19. Explain VTP versions.

Answer:

VTP version 1

  • Supports normal VLAN numbers (1-1005)
  • Support pruning of unused VLANs (no longer sends *Broadcasts and unknown unicasts
  • Transparent mode switch does not relay VTP information it receives to other switches unless it’s

VTP domain name & VTP version numbers match those of the other switches.

VTP version 2

  • Supports normal VLAN numbers (1-1005)
  • Forwards the VTP messages without checking  version number or domain in transparent

mode

  • Supports Token Ring
  • Performs consistency check on  VTP / VLAN parameters (from CLI or SNMP)
  • Pass on Unrecognised TLVs

VTP version 3

  • Supports extended VLAN numbers (1-4094)
  • Transfer information regarding Private VLAN structure
  • Support for databases other than VLAN .
  • Protection from unintended database overrides during the insertion of other switches.

 

20.Define Port cost ?

Answer :

Port price determines the best path when multiple links are used between two switches and none of the links is a root port. The cost of a link is set by the bandwidth of a link.

Author:

Shinde, Dnyaneshwari | SevenMentor Pvt. Ltd.

 

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